Secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, negative electrode wiring connected to the negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer and a coating covering the surface of the negative electrode active material layer. The coating contains sulfur as a constituent element. The electrolyte contains chain-like carboxylic acid esters. When the coating is divided into three equal parts—a first coating portion, a second coating portion, and a third coating portion—in a direction away from the negative electrode wiring, the sulfur content of at least one of the first coating portion and the third coating portion is 11 μmol / m³. 2 Above and 22 μmol / m 2 The sulfur content in the second coating section is 7 μmol / m. 2 Above and 13 μmol / m 2 In the following cases, the ratio of the sulfur content of at least one of the first coating portion and the third coating portion to the sulfur content of the second coating portion is 1.2 or more and 2.1 or less.

Description

Technical Field

[0001] This technology relates to a secondary battery. Background Technology

[0002] With the widespread adoption of mobile phones and other electronic devices, the development of secondary batteries—small, lightweight power sources capable of delivering high energy density—is underway. These secondary batteries possess a positive electrode, a negative electrode, and an electrolyte, and various studies have been conducted regarding their structure.

[0003] Specifically, in order to reduce internal resistance, a film derived from a sulfonic acid compound is formed on the surface of the positive electrode active material in a specified amount, and a mixed film derived from a sulfonic acid compound and vinylene carbonate in a specified amount is formed on the surface of the negative electrode active material (for example, see Patent Document 1).

[0004] Similarly, in order to reduce internal resistance, a specified amount of coating derived from lithium salt having a sulfonic acid backbone is formed on the surface of the positive electrode active material, and a specified amount of coating derived from vinylene carbonate is formed on the surface of the negative electrode active material (for example, see Patent Document 2).

[0005] In order to reduce the amount of gas generated during high-temperature storage, a first coating derived from dilithium disulfonate is formed on the surface of the positive electrode active material, and a second coating derived from dilithium disulfonate and vinylene carbonate in a specified amount is formed on the surface of the negative electrode active material (for example, see Patent Document 3).

[0006] In order to suppress the increase in resistance with long-term storage, a coating containing a specified amount of sulfur is formed on the surface of the positive electrode active material (for example, see Patent Document 4).

[0007] To improve cycling and storage properties, the electrolyte contains a cyclic sulfone compound having -S(=O)2-OS(=O)2- (for example, see Patent Document 5).

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2008-098053

[0011] Patent Document 2: Japanese Patent Application Publication No. 2014-232705

[0012] Patent Document 3: Japanese Patent Application Publication No. 2016-091724

[0013] Patent Document 4: Japanese Patent Application Publication No. 2017-010637

[0014] Patent Document 5: Japanese Patent Application Publication No. 2019-016483 Summary of the Invention

[0015] Various studies have been conducted to improve the performance of the secondary battery, but there is still room for improvement because the resistance and cycle characteristics of the secondary battery are not yet fully developed.

[0016] Therefore, there is a need for secondary batteries that can achieve excellent resistance characteristics and excellent cycle performance.

[0017] One embodiment of this technology provides a secondary battery comprising a positive electrode, a negative electrode, a negative electrode wiring connected to the negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer and a coating covering the surface of the negative electrode active material layer. The coating contains sulfur as a constituent element, and the electrolyte contains a chain-like carboxylic acid ester. When the coating is divided into three equal parts—a first coating portion, a second coating portion, and a third coating portion—in a direction away from the negative electrode wiring, the sulfur content of at least one of the first coating portion and the third coating portion is 11 μmol / m³. 2 Above and 22 μmol / m 2 The sulfur content in the second coating section is 7 μmol / m. 2 Above and 13 μmol / m 2 In the following cases, the ratio of the sulfur content of at least one of the first coating portion and the third coating portion to the sulfur content of the second coating portion is 1.2 or more and 2.1 or less.

[0018] According to one embodiment of the present technology, in a secondary battery, the negative electrode coating contains sulfur as a constituent element, and the electrolyte contains a chain-like carboxylic acid ester. Furthermore, in the coatings (first coating portion, second coating portion, and third coating portion), the sulfur content of at least one of the first and third coating portions, the sulfur content of the second coating portion, and the ratio of the sulfur content of at least one of the first and third coating portions to the sulfur content of the second coating portion satisfy the conditions described above. Therefore, excellent resistance characteristics and excellent cycle characteristics can be obtained.

[0019] It should be noted that the effect of this technology is not limited to the effect described herein, but can be any of the series of effects associated with this technology described later. Attached Figure Description

[0020] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0021] Figure 2 It means Figure 1 The diagram shows a cross-sectional view of the structure of the battery element.

[0022] Figure 3It means Figure 2 The diagram shows a top view of the negative electrode structure.

[0023] Figure 4 This is a perspective view illustrating the manufacturing process (stabilization treatment) of a secondary battery in one embodiment of the present technology.

[0024] Figure 5 This is a three-dimensional diagram showing the structure of the secondary battery in Modified Example 1.

[0025] Figure 6 It means Figure 5 The diagram shows a cross-sectional view of the structure of the battery element.

[0026] Figure 7 It means Figure 6 The diagram shows a top view of the negative electrode structure.

[0027] Figure 8 This is a perspective view used to illustrate the manufacturing process (stabilization treatment) of the secondary battery in Modified Example 1.

[0028] Figure 9 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0029] Hereinafter, with reference to the accompanying drawings, one embodiment of the present technology will be described in detail. It should be noted that the description is presented in the following order.

[0030] 1. Secondary battery

[0031] 1-1. Structure

[0032] 1-2.Physical properties

[0033] 1-3. Actions

[0034] 1-4. Manufacturing Method

[0035] 1-5. Functions and Effects

[0036] 2. Variations

[0037] 3. Uses of secondary batteries

[0038] <1. Secondary Battery>

[0039] First, a secondary battery according to one embodiment of this technology will be described.

[0040] The secondary battery described herein is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants, and it includes a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, in order to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode.

[0041] There are no particular restrictions on the types of substances used in the electrode reactions. Specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0042] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0043] <1-1. Structure>

[0044] Figure 1 The three-dimensional structure of a secondary battery is shown. Figure 2 It shows Figure 1 The cross-sectional structure of the battery element 20 shown. Figure 3 It shows Figure 2 The negative electrode 22 is shown as a planar structure.

[0045] in addition, Figure 1 The outer packaging film 10 and the battery element 20 are shown in a state where they are separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown in dashed lines. Figure 2 Only a portion of battery element 20 is shown. Figure 3 The diagram shows the state where the negative lead 32 is connected to the negative terminal 22.

[0046] like Figures 1-3 As shown, the secondary battery includes an outer packaging film 10, a battery element 20, a positive electrode lead 31 and a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or pliable) outer packaging film 10.

[0047] [Outer packaging film and sealing film]

[0048] like Figure 1 As shown, the outer packaging film 10 is a flexible outer packaging component that houses the battery element 20, and has a bag-like structure that is sealed when the battery element 20 is housed inside. Therefore, the outer packaging film 10 houses the positive electrode 21 and the negative electrode 22, as well as the electrolyte, which will be described later.

[0049] Here, the outer packaging film 10 is a thin film component that can be folded in the folding direction R. A recess 10U (so-called deep stretch portion) for accommodating the battery element 20 is provided on the outer packaging film 10.

[0050] Specifically, the outer packaging film 10 is a laminated film consisting of three layers stacked sequentially from the inside: a welding layer, a metal layer, and a surface protective layer. When the outer packaging film 10 is folded, the outer peripheries of the opposing welding layers are welded together. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0051] Furthermore, the structure (number of layers) of the outer packaging film 10 is not particularly limited; it can be one layer, two layers, or four or more layers. Additionally, when the outer packaging film 10 is a multi-layered laminated film, the material of each layer can be chosen arbitrarily.

[0052] Sealing film 41 is inserted between outer packaging film 10 and positive lead 31, and sealing film 42 is inserted between outer packaging film 10 and negative lead 32. Alternatively, one or both of sealing films 41 and 42 may be omitted.

[0053] The sealing film 41 is a sealing component that prevents external gases from entering the interior of the outer packaging film 10. Furthermore, the sealing film 41 contains a polymer compound such as a polyolefin, which has a sealing effect on the positive electrode lead 31. This polyolefin is polypropylene, etc.

[0054] Aside from being a sealing component that provides a tight seal for the negative electrode lead 32, the structure of the sealing membrane 42 is the same as that of the sealing membrane 41. That is, the sealing membrane 42 contains a polymer compound such as polyolefin that provides a tight seal for the negative electrode lead 32.

[0055] [Battery Components]

[0056] like Figures 1-3 As shown, the battery element 20 is a power generation element that includes a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown), and is housed inside the outer packaging film 10.

[0057] Here, the battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with a separator 23 in between, and the positive electrode 21, the negative electrode 22 and the separator 23 are wound around a winding axis P, which is an imaginary axis extending in the Y-axis direction. Thus, the positive electrode 21 and the negative electrode 22 are wound opposite each other with the separator 23 in between.

[0058] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the cross-section of the battery element 20 intersecting the winding axis P (the cross-section along the XZ plane) has a flat shape defined by the major axis J1 and the minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and having a length greater than the minor axis J2, and the minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and having a length less than the major axis J1. Here, the three-dimensional shape of the battery element 20 is a flattened cylindrical shape, therefore the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0059] (positive electrode)

[0060] like Figure 2 As shown, the positive electrode 21 includes a positive current collector 21A and a positive active material layer 21B.

[0061] The positive current collector 21A has one side on which a positive active material layer 21B is disposed, and supports the positive active material layer 21B. The positive current collector 21A contains a conductive material such as a metal, which is aluminum or the like.

[0062] Here, the positive electrode active material layer 21B is disposed on both sides of the positive electrode current collector 21A, and contains any one or more positive electrode active materials capable of lithium intercalation and deintercalation. Alternatively, the positive electrode active material layer 21B may be disposed on only one side of the positive electrode current collector 21A. Furthermore, the positive electrode active material layer 21B may also contain any one or more other materials such as a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited; specifically, it may be any one or more methods such as coating.

[0063] There are no particular limitations on the type of positive electrode active material; specifically, it can be lithium-containing compounds. These lithium-containing compounds are compounds that contain one or more transition metal elements as constituent elements along with lithium, and may also contain one or more other elements as constituent elements. The other elements can be any elements other than lithium and the transition metal elements; there are no particular limitations. Specifically, they must belong to groups 2 to 15 of the long-period periodic table. There are no particular limitations on the type of lithium-containing compound; specifically, it can be oxides, phosphoric acid compounds, silicate compounds, and borate compounds, etc.

[0064] Specific examples of oxides are LiNiO2, LiCoO2, and LiCo. 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 O2 and LiMn2O4, etc. Specific examples of phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0065] The positive electrode binder contains one or more of the following: synthetic rubber and polymeric compounds. Synthetic rubbers include styrene-butadiene rubber, fluorinated rubber, and ethylene propylene diene monomer (EPDM) rubber. Polymeric compounds include polyvinylidene fluoride (PVDF), polyimide, and carboxymethyl cellulose.

[0066] The positive electrode conductive agent contains one or more of the following conductive materials: carbon materials, such as graphite, carbon black, acetylene black, and Ketjen black. Alternatively, the conductive material can also be a metallic material or a polymer compound.

[0067] (negative electrode)

[0068] like Figure 2 As shown, the negative electrode 22 includes a negative electrode current collector 22A, a negative electrode active material layer 22B, and a coating 22C.

[0069] The negative current collector 22A has one side with a negative active material layer 22B disposed thereon, supporting the negative active material layer 22B. The negative current collector 22A contains a conductive material such as a metal, which is copper or the like.

[0070] Here, the negative electrode active material layer 22B is disposed on both sides of the negative electrode current collector 22A, and contains any one or more negative electrode active materials capable of lithium insertion / extraction. Alternatively, the negative electrode active material layer 22B may be disposed on only one side of the negative electrode current collector 22A. Furthermore, the negative electrode active material layer 22B may also contain any one or more other materials such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited; specifically, it may be any one or more of coating, vapor phase, liquid phase, spraying, and sintering methods.

[0071] The type of negative electrode active material is not particularly limited; specifically, it can be one or both of carbon materials and metallic materials. This is because high energy density can be obtained. Specific examples of carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite (natural and artificial graphite). Metallic materials are a general term for materials containing one or more metallic elements and half-metallic elements that can form alloys with lithium as constituent elements. These metallic elements and half-metallic elements are one or both of silicon and tin. Metallic materials can be elements, alloys, compounds, mixtures of two or more of them, or materials containing two or more of their phases. Specific examples of metallic materials are TiSi2 and SiO. x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0072] The details regarding the negative electrode binder and negative electrode conductive agent are the same as those regarding the positive electrode binder and positive electrode conductive agent.

[0073] The coating 22C covers the surface of the negative electrode active material layer 22B. In this case, the coating 22C may cover the entire surface of the negative electrode active material layer 22B, or it may only cover a portion of the surface of the negative electrode active material layer 22B. Alternatively, in the latter case, multiple coatings 22C that are isolated from each other may cover the surface of the negative electrode active material layer 22B. Figure 2 The diagram shows the situation where the coating 22C covers the entire surface of the negative electrode active material layer 22B.

[0074] As described later, the coating 22C is formed on the surface of the negative electrode active material layer 22B during the stabilization treatment (initial charge-discharge treatment) of the assembled secondary battery in the secondary battery manufacturing process, and contains sulfur as a constituent element.

[0075] Here, as described later, the electrolyte contains sulfur-containing compounds. Therefore, due to the decomposition and reaction of these sulfur-containing compounds during the aforementioned stabilization treatment, the coating 22C contains sulfur derived from these sulfur-containing compounds as a constituent element. These sulfur-containing compounds are a general term for compounds containing sulfur as a constituent element, and are substances that serve as a source of sulfur. Details regarding these sulfur-containing compounds will be described later.

[0076] In this secondary battery, the coating 22C meets specified physical property conditions to improve both the resistance and cycle characteristics. Details regarding the physical properties of the coating 22C will be described later.

[0077] (Diaphragm)

[0078] like Figure 2As shown, the separator 23 is an insulating porous membrane located between the positive electrode 21 and the negative electrode 22, which prevents contact (short circuit) between the positive electrode 21 and the negative electrode 22 while allowing lithium ions to pass through. The separator 23 contains polymer compounds such as polyethylene.

[0079] (Electrolyte)

[0080] An electrolyte is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0081] The solvent contains one or more chain carboxylic acid esters as non-aqueous solvents (organic solvents). This is because chain carboxylic acid esters have low viscosity, thus improving the ionic conductivity of the electrolyte (lithium-ion conductivity). Consequently, high-rate charging and discharging (large charging current and large discharging current) is improved, so the battery capacity is not easily reduced even when the secondary battery is charged and discharged at high rates. Electrolytes containing non-aqueous solvents (chain carboxylic acid esters) are called non-aqueous electrolytes.

[0082] There are no particular limitations on the types of chain carboxylic acid esters. Specifically, they include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, and isoethyl butyrate, etc. This is because it can significantly improve the ionic conductivity of the electrolyte. There are no particular limitations on the content of chain carboxylic acid esters in the solvent. Specifically, it should be 30% by volume or more. This is because it can further improve the ionic conductivity of the electrolyte.

[0083] The preferred chain carboxylic esters are ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate. This is because they can further improve the ionic conductivity of the electrolyte.

[0084] The solvent may also contain one or more other non-aqueous solvents. The types of other non-aqueous solvents are not particularly limited, but specifically include carbonate compounds and lactone compounds. Carbonate compounds include cyclic carbonates and chain carbonates, and lactone compounds include lactones.

[0085] It should be noted that the solvent may contain any one or more sulfur-containing compounds. This is because, during the stabilization treatment of the secondary battery, due to the decomposition and reaction of sulfur-containing compounds, a sulfur-containing coating 22C is easily formed on the surface of the negative electrode active material layer 22B. Furthermore, even if part of the coating 22C decomposes during charging and discharging, additional coating 22C is easily formed during subsequent charging and discharging due to the decomposition and reaction of sulfur-containing compounds.

[0086] As mentioned above, sulfur-containing compounds are substances that serve as a source of sulfur (compounds containing sulfur as a constituent element). These sulfur-containing compounds can be cyclic or chain-like. Furthermore, sulfur-containing compounds can contain one or both of the following: carbon-carbon double bonds and carbon-carbon triple bonds, which are unsaturated carbon bonds.

[0087] The types of sulfur-containing compounds are not particularly limited, but specifically they include cyclic sulfonates, chain sulfonates, cyclic disulfonic anhydrides, and cyclic sulfonic acid carboxylic anhydrides. This is because the coating 22C can easily and sufficiently form on the surface of the negative electrode active material layer 22B. The content of sulfur-containing compounds in the electrolyte is not particularly limited, and therefore can be set arbitrarily.

[0088] Specific examples of cyclic sulfonates are propane sulfonyl lactone (1,3-propane sulfonyl lactone), propene sulfonyl lactone (1-propene 1,3-sulfonyl lactone), 4-methyl-1,3,2-dioxazothiophene 2,2-dioxide, and 1,3,2-dioxazothiophene 2,2-dioxide, etc.

[0089] Specific examples of chain sulfonates include propargyl methanesulfonate, propargyl ethanesulfonate, and 2-propargyl benzenesulfonate.

[0090] Cyclic disulfonic anhydrides include ethane disulfonic anhydride and propane disulfonic anhydride, among others.

[0091] Specific examples of cyclic sulfonic acid carboxylic anhydrides include sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

[0092] The electrolyte salt contains one or more of light metal salts, such as lithium salts. The content of the electrolyte salt in the electrolyte is not particularly limited and can therefore be set arbitrarily.

[0093] [Positive and negative leads]

[0094] like Figure 1 As shown, the positive lead 31 is a positive wiring connected to the battery element 20 (positive electrode 21) and extends from the inside of the outer packaging film 10 to the outside. The positive lead 31 contains a conductive material such as aluminum, and the shape of the positive lead 31 can be any of the following: a thin plate or a mesh.

[0095] like Figure 1 as well as Figure 3 As shown, the negative electrode lead 32 is the negative electrode wiring connected to the battery element 20 (negative electrode 22). Details regarding the connection between the negative electrode 22 and the negative electrode lead 32 will be described later. Here, the negative electrode lead 32 extends from the inside of the outer packaging film 10 to the outside in the same direction as the positive electrode lead 31. This negative electrode lead 32 contains a conductive material such as copper, and the details regarding its shape are the same as those regarding the shape of the positive electrode lead 31.

[0096] <1-2.Physical Properties>

[0097] In this secondary battery, as described above, the coating 22C, containing sulfur as a constituent element, meets specified physical property conditions in order to improve both the resistance characteristics and cycle characteristics. Hereinafter, the connection state between the negative electrode 22 and the negative electrode lead 32 will be explained, followed by an explanation of the physical property conditions of the coating 22C. In this case, please refer to the previously explained... Figure 2 as well as Figure 3 .

[0098] [Connection status of negative terminal and negative terminal lead]

[0099] like Figure 2 As shown, the negative electrode 22 includes a negative electrode current collector 22A, a negative electrode active material layer 22B, and a coating 22C.

[0100] In this case, such as Figure 3 As shown, the negative electrode current collector 22A has a strip-like shape extending in the length direction (X-axis direction). Here, a negative electrode active material layer 22B is formed on the entire surface of the negative electrode current collector 22A, and a coating 22C covers the entire surface of the negative electrode active material layer 22B. Figure 3 In the middle, shading is drawn on the film 22C.

[0101] Here, the negative electrode lead 32 is separate from the negative electrode 22 (negative electrode current collector 22A). The negative electrode lead 32 extends in the width direction (Y-axis direction) intersecting the length direction and is partially connected to the negative electrode 22, such that the connection area between the negative electrode lead 32 and the negative electrode 22 is sufficiently small within an acceptable range. Thus, one end of the negative electrode lead 32 overlaps with one end of the negative electrode 22 in the width direction, thereby connecting to one end of the negative electrode 22. It should be noted that the other end of the negative electrode lead 32 does not overlap with one end of the negative electrode 22, but protrudes to the outside of the negative electrode 22 (negative electrode active material layer 22B).

[0102] In the region where the negative electrode and the negative electrode lead 32 overlap, the negative electrode active material layer 22B and the coating 22C are not formed on the surface of the negative electrode current collector 22A, thus the negative electrode current collector 22A is exposed. Therefore, the negative electrode lead 32 is connected to the negative electrode current collector 22A.

[0103] In the battery element 20, which serves as a wound electrode body, the position where the negative electrode lead 32 connects to the negative electrode 22 is not particularly limited. That is, when the negative electrode 22 is wound, the negative electrode lead 32 can be connected to the negative electrode 22 on the outside of the winding, on the inside of the winding, or along the path between the outside and inside of the winding. Figure 3In the diagram, the right side is the outer winding and the left side is the inner winding, thus showing the case where the negative lead 32 is connected to the negative electrode 22 on the inner winding side.

[0104] [Physical Properties]

[0105] Using the position of the negative electrode lead 32 connected to the negative electrode 22 as a reference, the coating 22C is divided into three equal parts in a direction away from the negative electrode lead 32 (along the width direction D). Thus, the coating 22C is classified into a coating portion 22C1 as a first coating portion, a coating portion 22C2 as a second coating portion, and a coating portion 22C3 as a third coating portion. In this case, the three physical property conditions described below are simultaneously satisfied.

[0106] (Physical property condition 1)

[0107] In the coated portions 22C1 to 22C3, the sulfur content X (μmol / m) in one or both of the coated portions 22C1 and 22C3, which are the two ends in the width direction, is... 2 ) is 11 μmol / m 2 ~22μmol / m 2 .

[0108] That is, under physical property condition 1, the sulfur content X in the coated portion 22C1 can be 11 μmol / m 2 ~22μmol / m 2 The sulfur content X in the coated portion 22C3 can be 11 μmol / m 2 ~22μmol / m 2 The sulfur content X in both the coated portions 22C1 and 22C3 can be 11 μmol / m 2 ~22μmol / m 2 .

[0109] As described later, when a portion of the battery element 20 (one or both of the coating portions 22C1 and 22C3) is heated during the stabilization treatment of the assembled secondary battery, the content X can be adjusted to a desired value by changing conditions such as heating temperature, heating time, and aging time after heating. Furthermore, the content X can also be adjusted to a desired value by changing the content of sulfur-containing compounds in the electrolyte.

[0110] (Physical property condition 2)

[0111] In the coated portions 22C1~22C3, the sulfur content Y (μmol / m) in the coated portion 22C2, which is the central portion in the width direction, is... 2 ) is 7 μmol / m 2 ~13μmol / m 2 .

[0112] The content Y can be adjusted to a desired value by changing the content of sulfur-containing compounds in the electrolyte. Similarly, as with adjusting the content X, the content Y can be adjusted to a desired value by heating a portion of the battery element 20 (coating portion 22C2) during the stabilization treatment of the secondary battery.

[0113] (Physical property condition 3)

[0114] The ratio of content X to content Y, i.e., the content ratio Z, is 1.2 to 2.1. This content ratio Z is calculated based on the formula: content ratio Z = content X / content Y.

[0115] (Reasons for satisfying physical property conditions 1-3)

[0116] Since physical property conditions 1 to 3 are satisfied simultaneously, in the negative electrode 22 containing the coating 22C, the amount of coating 22C formed at both ends (coating portions 22C1, 22C3) in the width direction (content X) is greater than the amount of coating 22C formed at the central portion (coating portion 22C2) in the width direction (content Y). In this case, the content ratio Z is optimized to be in the range of 1.2 to 2.1.

[0117] The reason why physical property conditions 1 to 3 are satisfied simultaneously is that, as explained later, the distribution of the amount of coating 22C formed in the negative electrode 22 is optimized when the electrolyte contains chain carboxylic acid esters. This suppresses the increase in resistance in the negative electrode 22 while improving the ionic conductivity of lithium ions, thus achieving a balance between suppressing the increase in resistance and improving ionic conductivity. Details of the reasons explained here will be described later.

[0118] [Calculation steps for content X, Y, and content ratio Z]

[0119] The contents X and Y were calculated based on the results of inductively coupled plasma (ICP) emission spectroscopy analysis of the coating 22C. The content ratio Z was determined based on the calculated results for both contents X and Y.

[0120] The specific calculation steps for the contents X, Y, and the content ratio Z are as follows.

[0121] First, the secondary battery is discharged until the voltage reaches 3V. The discharge current is not particularly limited and can be set arbitrarily. Next, the discharged secondary battery is disassembled, and the negative electrode 22 is recovered. Next, the negative electrode 22 is cleaned using a cleaning solvent. The type of cleaning solvent is not particularly limited; specifically, organic solvents such as dimethyl carbonate are used. Next, the negative electrode 22 is stamped into a disc shape (diameter = 19mm), thus obtaining the sample for analysis.

[0122] Next, the sample (coated 22C) is analyzed using an ICP-based spectrophotometer. In this case, the sulfur content (μg) in one or both of the coated portions 22C1 and 22C3 is determined by analyzing one or both of the coated portions 22C1 and 22C3. The ICP-based spectrophotometer can be an ICP-based spectrophotometer (sequential type) SPS3500 manufactured by HITACHI HI-TECH SCIENCE Co., Ltd. (formerly SII NANOTECHNOLOGY Co., Ltd.). Next, based on the sulfur content (converting μg to μmol) and the sample area (m²), the content X (μmol / m²) is calculated. 2 ).

[0123] Next, except for analyzing coating portion 22C2 instead of one or both of coating portions 22C1 and 22C3, the content Y (μmol / m) is calculated using the same steps. 2 ).

[0124] Finally, based on the contents X and Y, the content ratio Z (= content X / content Y) is calculated. Therefore, based on the analytical results of the coated 22C using ICP emission spectroscopy, the contents X, Y, and content ratio Z are calculated respectively.

[0125] <1-3. Actions>

[0126] During charging of the secondary battery, lithium is deintercalated from the positive electrode 21 in battery element 20 and intercalated into the negative electrode 22 via the electrolyte. Conversely, during discharging of the secondary battery, lithium is deintercalated from the negative electrode 22 in battery element 20 and intercalated into the positive electrode 21 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0127] <1-4. Manufacturing Method>

[0128] The secondary battery is manufactured using the steps described below. In this case, as described later, after assembling the secondary battery using positive electrode 21, negative electrode precursor, and electrolyte, a stabilization treatment is performed on the assembled secondary battery.

[0129] To illustrate the manufacturing process (stabilization treatment) of secondary batteries. Figure 4 It shows the corresponding Figure 1 Its three-dimensional structure. Additionally, in Figure 4 In order to make it easier to understand the heating range of the winding body 20Z, the illustrations of the outer packaging film 10 and the sealing films 41 and 42 are omitted.

[0130] [The production of the positive electrode]

[0131] A positive electrode active material is mixed with a positive electrode binder and a positive electrode conductive agent as needed to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent to prepare a paste-like positive electrode mixture slurry. This solvent can be an aqueous solvent or a non-aqueous solvent (organic solvent). Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 21A to form a positive electrode active material layer 21B. Subsequently, the positive electrode active material layer 21B can be compressed and molded using a roller press or the like. In this case, the positive electrode active material layer 21B can be heated, or the compression molding can be repeated multiple times. Thus, the positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby producing the positive electrode 21.

[0132] [Making the negative electrode]

[0133] Following the same steps as those used in the fabrication of the positive electrode 21 described above, negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A. Specifically, the negative electrode active material is mixed with a negative electrode binder and a negative electrode conductive agent as needed to prepare a negative electrode mixture. This mixture is then added to a solvent to prepare a paste-like negative electrode mixture slurry. Details regarding the solvent are as described above. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 22A, thereby forming the negative electrode active material layers 22B. Subsequently, the negative electrode active material layers 22B can be compressed and molded. Thus, negative electrode active material layers 22B are formed on both sides of the negative electrode current collector 22A, thereby producing a negative electrode precursor (not shown).

[0134] Finally, as described later, after assembling the secondary battery using the negative electrode precursor, a stabilization treatment is performed on the assembled secondary battery. This forms a coating 22C containing sulfur as a constituent element on the surface of the negative electrode active material layer 22B. Thus, the negative electrode active material layer 22B and the coating 22C are formed on both sides of the negative electrode current collector 22A, thereby forming the negative electrode 22.

[0135] (Preparation of electrolyte)

[0136] After the electrolyte salt is added to the solvent, a sulfur-containing compound is added to the solvent. The type of solvent is not particularly limited; specifically, it can be a non-aqueous solvent (organic solvent), etc. Thus, the electrolyte salt and the sulfur-containing compound are dispersed or dissolved in the solvent, thereby preparing the electrolyte solution.

[0137] (Assembly of secondary batteries)

[0138] First, the positive lead 31 is connected to the positive electrode 21 (positive current collector 21A) using a soldering method or the like, and the negative lead 32 is connected to the negative electrode 22 (negative current collector 22A) using a soldering method or the like.

[0139] Next, the positive electrode 21 and the negative electrode precursor are stacked on top of each other through the diaphragm 23, and then the positive electrode 21, the negative electrode precursor, and the diaphragm 23 are wound together, thus... Figure 4 As shown, a wound body 20Z is fabricated. This wound body 20Z has the same structure as the battery element 20, except that it has a negative electrode precursor instead of a negative electrode 22, and the positive electrode 21, negative electrode precursor, and separator 23 are not impregnated with electrolyte. Next, the wound body 20Z is formed into a flat shape by pressing it with a press or the like.

[0140] Next, after housing the wound body inside the recess 10U, the outer packaging film 10 (welding layer / metal layer / surface protective layer) is folded so that the outer packaging films 10 are facing each other. Next, the outer periphery portions of two sides of the opposing outer packaging films 10 (welding layers) are welded together using a heat fusion method or the like, thereby housing the wound body 20Z inside the bag-shaped outer packaging film 10.

[0141] Finally, after injecting the electrolyte into the pouch-shaped outer packaging film 10, the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is fused together using a heat fusion method or the like. In this case, a sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, the electrolyte is impregnated in the wound body 20Z, and the wound body 20Z is sealed inside the pouch-shaped outer packaging film 10, thereby assembling a secondary battery.

[0142] (Stabilization of secondary batteries)

[0143] The assembled secondary battery is charged and discharged. Ambient temperature, number of charge / discharge cycles, and charging / discharging conditions can be arbitrarily set. This causes the sulfur-containing compounds in the electrolyte to decompose and react, thereby forming a coating 22C containing sulfur as a constituent element on the surface of the negative electrode active material layer 22B. Thus, by forming the negative electrode active material layer 22B and the coating 22C on both sides of the negative electrode current collector 22A, the negative electrode 22 is fabricated, thereby fabricating the battery element 20.

[0144] In this case, heating equipment such as heaters is used to locally heat the wound body 20Z. Specifically, such as... Figure 3 as well as Figure 4 As shown, in the wound body 20Z, which includes a winding portion 201 corresponding to the coating portion 22C1, a winding portion 202 corresponding to the coating portion 22C2, and a winding portion 203 corresponding to the coating portion 22C3, one or both of the winding portions 201 and 203 are heated. The heating conditions are not particularly limited; specifically, the heating temperature is 60°C to 80°C, and the heating time is 1 hour to 24 hours.

[0145] Through this heat treatment, the amount of coating 22C formed increases in one or both of the winding sections 201 and 203. On the other hand, in the winding section 202 where no heat treatment is performed, the amount of coating 22C formed does not increase. In this case, by changing the heating conditions described above, the contents X and Y can be controlled separately, and therefore the content ratio Z can also be controlled.

[0146] Thus, since the assembled secondary battery is electrochemically stable, the secondary battery using the outer packaging film 10 is completed, namely, the laminated film type secondary battery.

[0147] It should be noted that the secondary battery can also be aged after the stabilization treatment is completed. There are no particular limitations on the aging conditions; specifically, the aging temperature is 60℃~80℃, and the aging time is 6 hours~48 hours. By changing these aging conditions, the contents of X and Y can be controlled separately, and therefore the content ratio Z can also be controlled.

[0148] In addition, after the stabilization treatment of the secondary battery is completed, that is, after the negative electrode 22 is made (a coating 22C is formed on the surface of the negative electrode active material layer 22B), the sulfur-containing compound used to form the coating 22C may remain in the electrolyte or may not remain in the electrolyte.

[0149] <1-5. Functions and Effects>

[0150] According to this secondary battery, the coating 22C of the negative electrode 22 contains sulfur as a constituent element, and the electrolyte contains chain-like carboxylic acid esters. Furthermore, in the coating 22C (coating portions 22C1~22C3), physical property conditions 1~3 are simultaneously satisfied (content X = 11 μmol / m). 2 ~22μmol / m 2 Content Y = 7 μmol / m 2 ~13μmol / m 2 (Containing a ratio Z = 1.2~2.1). Therefore, for the reasons explained below, excellent resistance characteristics and excellent cycling characteristics can be obtained.

[0151] In detail, because the electrolyte contains chain carboxylic acid esters as a low-viscosity solvent, the ionic conductivity of lithium ions in the electrolyte is improved. As a result, since lithium ions are easily inserted and extracted in the negative electrode 22 during charging and discharging, the cycle characteristics are improved, and in particular, excellent cycle characteristics can be obtained even when the secondary battery is charged and discharged at a high rate.

[0152] However, due to the high volatility of chain carboxylic esters as low-viscosity solvents, they tend to evaporate easily during long-term use (long-term storage) of secondary batteries. In particular, the volatility of the chain carboxylic esters is more pronounced at the two ends (coated portions 22C1 and 22C3) of the negative electrode 22, which are more susceptible to contact with external air, compared to the middle portion (coated portion 22C2) of the negative electrode 22, which is less likely to come into contact with external air. That is, the amount of chain carboxylic ester evaporating in each of the coated portions 22C1 and 22C3 is greater than the amount evaporating in the coated portion 22C2.

[0153] When the chain carboxylic esters volatilize in the coated portions 22C1 and 22C3, respectively, the viscosity of the electrolyte increases. As a result, the ionic conductivity of lithium ions in the electrolyte decreases, making it easier for lithium metal to deposit on the surface of the negative electrode 22.

[0154] Here, when a coating 22C containing sulfur as a constituent element is formed on the surface of the negative electrode active material layer 22B, the surface of the negative electrode 22 is protected by the coating 22C, so lithium metal is less likely to deposit on the surface of the negative electrode 22. However, when the coating 22C is formed on the surface of the negative electrode active material layer 22B, lithium metal is less likely to deposit, but on the other hand, the internal resistance of the secondary battery (negative electrode 22) increases, so the final cycle characteristics are reduced. In particular, the cycle characteristics are significantly reduced when the secondary battery is charged and discharged at a high rate.

[0155] Based on the above, when the electrolyte contains chain carboxylic acid esters but no coating 22C is formed on the surface of the negative electrode active material layer 22B, the following trade-off occurs: the resistance characteristics are improved due to the absence of the coating 22C, but the cycle characteristics are reduced due to the easy deposition of lithium metal. In other words, a relationship arises where one characteristic is improved while the other characteristic is reduced.

[0156] Furthermore, when a coating 22C is formed on the surface of the negative electrode active material layer 22B, but the electrolyte does not contain chain carboxylic acid esters, the following trade-off occurs: the cycle characteristics are improved because lithium metal is less likely to be deposited, but the resistance characteristics are reduced due to the presence of the coating 22C.

[0157] In contrast, when the electrolyte contains chain carboxylic acid esters and a coating 22C is formed on the surface of the negative electrode active material layer 22B, the distribution of the amount of coating 22C formed is optimized as described above when physical property conditions 1 to 3 are simultaneously satisfied. That is, the amount of coating 22C formed in one or both of the coating portions 22C1 and 22C3 is appropriately greater than the amount of coating 22C formed in the coating portion 22C3.

[0158] In this case, lithium metal is less likely to deposit due to the presence of one or both of the coating portions 22C1 and 22C3, thus improving cycle characteristics. Moreover, even if the coating portion 22C3 is present, its resistance is less likely to increase, thus improving resistance characteristics.

[0159] Based on the above, by simultaneously satisfying physical property conditions 1 to 3, the aforementioned trade-off is broken, thus suppressing the increase in resistance characteristics and improving cycle characteristics. In this case, of course, the same tendency can be obtained even when the secondary battery is charged and discharged at high rates. Therefore, excellent resistance characteristics and excellent cycle characteristics can be obtained.

[0160] In particular, if the chain carboxylic acid ester contains ethyl acetate, the ionic conductivity of the electrolyte is significantly improved, thus achieving even better results.

[0161] Furthermore, if the electrolyte contains sulfur-containing compounds, a sulfur-containing coating 22C is easily formed on the surface of the negative electrode active material layer 22B, thus achieving higher performance. In this case, if the electrolyte also contains sulfur-containing compounds after the stabilization treatment of the secondary battery (after the formation of the coating 22C), additional coating 22C is easily formed during charge and discharge after the stabilization treatment, thus achieving even higher performance. Additionally, if the sulfur-containing compound contains cyclic sulfonates or the like, the coating 22C is easily and sufficiently formed on the surface of the negative electrode active material layer 22B, thus achieving even higher performance.

[0162] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0163] <2. Variations>

[0164] As explained below, the structure of the secondary battery can be appropriately modified. Furthermore, any two or more of the variations described below can be combined with each other.

[0165] [Variation Example 1]

[0166] exist Figures 1-3 In this secondary battery, a battery element 20 is provided as a wound electrode body. However, as corresponding to Figures 1-3 of Figures 5-7 As shown, the secondary battery may also have a battery element 50 as a stacked electrode body instead of a battery element 20 as a wound electrode body.

[0167] Figures 5-7The laminated film type secondary battery shown, in addition to having battery element 50 (positive electrode 51, negative electrode 52, and separator 53), positive electrode lead 61, and negative electrode lead 62 replacing battery element 20 (positive electrode 21, negative electrode 22, and separator 23), positive electrode lead 31, and negative electrode lead 32, has the same... Figures 1-3 The structure shown is the same as that of the laminated film type secondary battery.

[0168] Except as described below, the structures of the positive electrode 51, the negative electrode 52, and the separator 53 are the same as those of the positive electrode 21, the negative electrode 22, and the separator 23.

[0169] In battery element 50, positive electrode 51 and negative electrode 52 are alternately stacked with a separator 53 in between. The number of layers for each of the positive electrode 51, negative electrode 52, and separator 53 is not particularly limited. Positive electrode 51 includes positive current collector 51A and positive active material layer 51B corresponding to positive current collector 21A and positive active material layer 21B. Negative electrode 52 includes negative current collector 52A, negative active material layer 22B, and coating 22C corresponding to negative current collector 22A, negative active material layer 22B, and coating 22C. The electrolyte composition is as described above.

[0170] In addition, such as Figure 5 as well as Figure 7 As shown, the positive current collector 51A and the negative current collector 52A are both rectangular sheets. The positive current collector 51A includes a protrusion 51AT without a positive active material layer 51B, and the negative current collector 52A includes a protrusion 52AT without a negative active material layer 52B. The protrusions 52AT are positioned to not overlap with the protrusions 51AT. Multiple protrusions 51AT are joined together to form a lead-shaped positive wiring, i.e., a positive lead 61, and multiple protrusions 52AT are joined together to form a lead-shaped negative wiring, i.e., a negative lead 62. That is, the positive lead 61 connected to the positive electrode 51 is integrated with the positive current collector 51A, and the negative lead 62 connected to the negative electrode 52 is integrated with the negative current collector 62A.

[0171] In battery element 50, similarly to battery element 20 described above, physical property conditions 1 to 3 are simultaneously satisfied. Specifically, taking the position of the negative electrode lead 62 connected to the negative electrode 52 as a reference, the coating 52C is divided into three equal parts (coated portions 52C1 to 52C3) in a direction D away from the negative electrode lead 62. In this case, the sulfur content X in one or both of the coated portions 52C1 and 52C3 is 11 μmol / m³. 2 ~22μmol / m 2 (Physical property condition 1). The sulfur content Y in the coated portion 52C2 is 7 μmol / m 2 ~13μmol / m2 (Physical property condition 2). The ratio of content X to content Y, i.e., the content ratio Z, is 1.2~2.1 (Physical property condition 3).

[0172] Figures 5-7 The manufacturing method of the laminated film type secondary battery shown includes, in addition to, the method corresponding to Figure 4 of Figure 8 As shown, apart from fabricating a laminate 50Z instead of a wound body 20Z and performing stabilization treatment on a secondary battery assembled using the laminate 50Z, and... Figures 1-4 The manufacturing method is the same as that of the laminated film type secondary battery shown.

[0173] In manufacturing the battery element 50, firstly, a positive electrode 51 is formed with a positive electrode active material layer 51B on both sides (except for the protrusion 51AT) of the positive electrode current collector 51A, and a negative electrode 52 is formed with a negative electrode active material layer 52B on both sides (except for the protrusion 52AT) of the negative electrode current collector 52A. Next, as follows... Figure 8 As shown, positive electrode 51 and negative electrode 52 are alternately stacked with a diaphragm 53 in between, thereby forming a laminate 50Z. Thereafter, the protrusions 51AT are joined together with each other by means of welding, thereby forming a positive electrode lead 61, and the protrusions 52AT are joined together with each other by means of welding, thereby forming a negative electrode lead 62.

[0174] In the stabilization treatment of the assembled secondary battery, heating equipment such as heaters is used to locally heat the laminate 50Z. Specifically, such as... Figure 8 As shown, one or both of the laminates 501 and 503 in the laminate 50Z, which includes the laminate 501 corresponding to the coating portion 52C1, the laminate 502 corresponding to the coating portion 52C2, and the laminate 503 corresponding to the coating portion 52C3, are heated. This forms a coating 52C containing sulfur as a constituent element on the surface of the negative electrode active material layer 52B, thereby producing the negative electrode 52 and the battery element 50. In this case, by changing the heating conditions described above, the contents X and Y can be controlled separately, and therefore the content ratio Z can also be controlled.

[0175] When using the battery element 50 as the stacked electrode body, since physical property conditions 1 to 3 are satisfied simultaneously, the same effect as when using the battery element 20 as the wound electrode body can be obtained. That is, excellent resistance characteristics and excellent cycle characteristics can be obtained.

[0176] [Variation Example 2]

[0177] A membrane 23, which is a porous membrane, was used. However, although not specifically illustrated here, a laminated membrane comprising layers of polymer compounds may be used instead of the porous membrane 23.

[0178] Specifically, the laminated separator includes a porous membrane with one and two faces and a polymer compound layer disposed on one or both faces of the porous membrane. This is because, due to the improved adhesion of the separator to each of the positive electrode 21 and the negative electrode 22, positional displacement of the battery element 20 (winding displacement of each of the positive electrode 21, negative electrode 22, and separator) is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less likely to expand. The polymer compound layer contains polymers such as polyvinylidene fluoride (PVDF). This is because PVDF and similar compounds have excellent physical strength and electrochemical stability.

[0179] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles dissipate heat when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles include inorganic particles and resin particles. Specific examples of inorganic particles include alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include acrylic resin and styrene resin.

[0180] In the case of fabricating a stacked membrane, a precursor solution containing a polymer compound and an organic solvent is prepared, and then the precursor solution is coated onto one or both sides of the porous membrane. In this case, multiple insulating particles can also be added to the precursor solution as needed.

[0181] With the use of this layered separator, lithium ions can also move between the positive electrode 21 and the negative electrode 22, thus achieving the same effect.

[0182] [Variation Example 3]

[0183] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel electrolyte, can also be used instead of an electrolyte solution.

[0184] In the battery element 20 using an electrolyte layer, after the positive electrode 21 and the negative electrode 22 are stacked together with the separator 23 and the electrolyte layer in between, the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound together. The electrolyte layer is located between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0185] Specifically, the electrolyte layer contains an electrolyte and a polymer compound, in which the electrolyte is held in place by the polymer compound. This is to prevent leakage. The structure of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In the case of forming the electrolyte layer, after preparing a precursor solution containing an electrolyte, a polymer compound, and an organic solvent, the precursor solution is coated on one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0186] When this electrolyte layer is used, lithium ions can also move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving the same effect.

[0187] <3. Uses of Secondary Batteries>

[0188] Next, we will explain the uses (application examples) of the aforementioned secondary batteries.

[0189] The uses of secondary batteries are not particularly limited. Secondary batteries used as power sources are the main power source or auxiliary power source for electronic devices and electric vehicles. The main power source is the power source used preferentially, regardless of the availability of other power sources. The auxiliary power source is the power source used in place of the main power source, or a power source switched from the main power source.

[0190] Specific examples of applications for rechargeable batteries are as follows: Electronic devices such as camcorders, digital still cameras, mobile phones, laptops, stereo headphones, portable radios, and portable information terminals. Backup power supplies and storage devices such as memory cards. Power tools such as electric drills and chainsaws. Battery packs integrated into electronic devices. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as household or industrial battery systems that pre-store power in preparation for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0191] Battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using secondary batteries as a power source, and can also be hybrid vehicles that have a power source other than the secondary battery. In home power storage systems, electricity stored in secondary batteries, which serve as power storage sources, can be used to operate household electrical products, etc.

[0192] Here, we will specifically illustrate one application example of a secondary battery. The structure of the application example described below is only one example and can therefore be modified as appropriate.

[0193] Figure 9 The frame structure of the battery pack is shown. The battery pack described here is a battery pack (so-called a pouch) that uses a secondary battery and is installed in electronic devices such as smartphones.

[0194] like Figure 9 As shown, the battery pack includes a power supply 71 and a circuit board 72. The circuit board 72 is connected to the power supply 71 and includes a positive terminal 73, a negative terminal 74, and a temperature detection terminal 75.

[0195] The power supply 71 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 73, and the negative lead is connected to the negative terminal 74. Since the power supply 71 can be connected to an external source via the positive terminal 73 and the negative terminal 74, it can be charged and discharged. The circuit board 72 includes a control unit 76, a switch 77, a thermistor element (PTC element) 78, and a temperature detection unit 79. Alternatively, the PTC element 78 may be omitted.

[0196] The control unit 76 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 76 detects and controls the operating status of the power supply 71 as needed.

[0197] It should be noted that when the voltage of the power supply 71 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, the control unit 76 cuts off the switch 77, thereby preventing the charging current from flowing through the current path of the power supply 71. The overcharge detection voltage and the over-discharge detection voltage are not particularly limited. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the over-discharge detection voltage is 2.4V ± 0.1V.

[0198] The switch 77 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between the power supply 71 and an external device according to the instruction of the control unit 76. The switch 77 includes a field-effect transistor (MOSFET) using metal-oxide-semiconductor, etc., and the charging and discharging current is detected based on the on-resistance of the switch 77.

[0199] The temperature detection unit 79 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 71 using the temperature detection terminal 75, and outputs the temperature measurement result to the control unit 76. The temperature measurement result measured by the temperature detection unit 79 is used for charging and discharging control by the control unit 76 when abnormal heating occurs, and for correction processing by the control unit 76 when calculating the remaining capacity. Example

[0200] The embodiments of this technology are described below.

[0201] <Examples 1-13 and Comparative Examples 1-9>

[0202] As described below, the battery characteristics of the secondary battery were evaluated after its manufacture.

[0203] [Manufacturing of secondary batteries]

[0204] The following steps were followed to manufacture... Figures 1-4 The image shows a laminated film type secondary battery (lithium-ion secondary battery).

[0205] (The production of the positive electrode)

[0206] First, 95 parts by mass of positive electrode active material, 4 parts by mass of positive electrode binder (polyvinylidene fluoride), and 1 part by mass of positive electrode conductive agent (graphite) are mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of a positive electrode current collector 21A (a strip of aluminum foil with a thickness of 15 μm) using a coating device, and then dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compressed and molded using a roller press. Thus, a positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby producing the positive electrode 21.

[0207] (Making the negative electrode)

[0208] First, 90 parts by mass of negative electrode active material (graphite) and 10 parts by mass of negative electrode binder (polyvinylidene fluoride) are mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of a negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating apparatus, and then dried to form a negative electrode active material layer 22B. Next, the negative electrode active material layer 22B is compressed and molded using a roller press. Thus, a negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, thereby producing a negative electrode precursor. Finally, as described later, after assembling a secondary battery using the negative electrode precursor, a stabilization treatment (initial charge-discharge treatment) is performed on the assembled secondary battery. Thus, a coating 22C containing sulfur as a constituent element is formed on the surface of the negative electrode active material layer 22B, thereby producing the negative electrode 22.

[0209] (Preparation of electrolyte)

[0210] The electrolyte salt (lithium hexafluorophosphate (LiPF6)) was added to the solvent, and the solvent was then stirred. Ethylene carbonate and propylene carbonate, as cyclic carbonates, and propyl propionate (PP), as a chain carboxylic acid ester, were used as solvents. In this case, the mixing ratio (volume ratio) of the solvents was ethylene carbonate : propylene carbonate : chain carboxylic acid ester = 10 : 20 : 70, and the content of the electrolyte salt relative to the solvent was 1 mol / kg.

[0211] Next, a sulfur-containing compound (propane sulfonyl lactone (PS) as a cyclic sulfonate) was added to a solvent containing an electrolyte salt, and the solvent was then stirred. In this case, the content of the sulfur-containing compound in the electrolyte was 1% by weight. Thus, an electrolyte containing a sulfur-containing compound was prepared.

[0212] (Assembly of secondary batteries)

[0213] First, the positive lead 31 (a strip of aluminum foil) is soldered to the positive electrode 21 (positive current collector 21A), and the negative lead 32 (a strip of copper foil) is soldered to the negative electrode precursor (negative current collector 22A).

[0214] Next, the positive electrode 21 and the negative electrode precursor are stacked together with the separator 23 (a microporous polyethylene membrane with a thickness of 25 μm) in between, and then the positive electrode 21, the negative electrode precursor and the separator 23 are wound together to form a wound body 20Z. Next, the wound body 20Z is stamped using a press to form a flat shape.

[0215] Next, the outer packaging film 10 is folded so that the wound body 20Z, which is housed inside the recess 10U, is sandwiched between the two outer peripheral edges of the outer packaging film 10. Then, the two outer peripheral edges of the outer packaging film 10 are heat-fused together, thereby housing the wound body 20Z inside the bag-shaped outer packaging film 10. The outer packaging film 10 is an aluminum laminate film in which a welding layer (30 μm thick polypropylene film), a metal layer (40 μm thick aluminum foil), and a surface protective layer (25 μm thick nylon film) are layered sequentially from the inside. In this case, the outer peripheral edges of the two opposing welding layers are heat-fused together.

[0216] Finally, after injecting the electrolyte into the pouch-shaped outer packaging film 10, the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 41 (a 5 μm thick polypropylene film) is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 (a 5 μm thick polypropylene film) is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, the winding body 20Z is impregnated with electrolyte, and the winding body 20Z is sealed inside the pouch-shaped outer packaging film 10, thereby assembling a secondary battery.

[0217] (Stabilization of secondary batteries)

[0218] Under normal temperature conditions (temperature = 25℃), the assembled secondary battery was subjected to one charge-discharge cycle. During charging, a constant current of 0.1C was used until the voltage reached 4.45V, followed by constant voltage charging at that 4.45V until the current reached 0.005C. During discharging, a constant current of 0.1C was used until the voltage reached 3.0V. 0.1C refers to the current required to fully discharge the battery (theoretical capacity) over 10 hours, and 0.005C refers to the current required to fully discharge the battery over 200 hours.

[0219] In this case, a portion of the wound body 20Z (wound portions 201 and 203) was heated using a heater. In this heat treatment, the heating temperature was varied within the range of 60°C to 80°C, and the heating time was varied within the range of 1 hour to 24 hours.

[0220] Thus, as described above, a coating 22C is formed on the surface of the negative electrode active material layer 22B in the negative electrode precursor, thereby fabricating the negative electrode 22. As a result, the battery element 20 is fabricated, and the state of the secondary battery is electrochemically stabilized, thus completing the laminated film type secondary battery.

[0221] After completing the secondary battery, it was disassembled to recover the negative electrode 22. The negative electrode 22 (coated 22C) was then analyzed using ICP emission spectroscopy to calculate the contents X and Y (μmol / m³). 2 The results shown in Tables 1 to 3 are obtained by considering the ratio Z.

[0222] In the manufacturing process of secondary batteries, the contents of X, Y, and the content ratio Z were adjusted by changing the heating conditions (heating temperature and heating time) during the stabilization treatment.

[0223] [Evaluation of Battery Characteristics]

[0224] The battery characteristics (resistance and cycle characteristics) of the secondary battery were evaluated, and the results are shown in Tables 1 to 3. Here, two cycle characteristics were evaluated as the cycle characteristics.

[0225] In investigating the resistance characteristics, firstly, the secondary battery was charged at room temperature (temperature = 23°C), and then its resistance (resistance before storage) was measured. The charging conditions were the same as those used during the stabilization treatment of the secondary battery described above. Next, the charged secondary battery was stored in a high-temperature environment (temperature = 60°C) for one month, and then its resistance (resistance after storage) was measured. Finally, based on the formula: resistance change rate = (resistance after storage / resistance before storage) × 100, the resistance change rate (%) was calculated as an indicator for evaluating the resistance characteristics.

[0226] In investigating the first type of cycle characteristics, firstly, the discharge capacity (discharge capacity of the first cycle) was measured by charging and discharging the secondary battery in a normal temperature environment (temperature = 23°C). Next, the secondary battery was placed in the same environment (placement time = 1 month). Then, the secondary battery was repeatedly charged and discharged in the same environment until the number of cycles (charge and discharge times) reached 100, and the discharge capacity (discharge capacity of the 100th cycle) was measured. Finally, based on the formula Capacity Retention Rate 1 = (Discharge capacity of the 100th cycle / Discharge capacity of the first cycle) × 100, the Capacity Retention Rate 1 (%), used as an indicator for evaluating cycle characteristics, was calculated. The charge and discharge conditions were the same as those used during the stabilization treatment of the secondary battery, except that the charging current and the discharging current were changed to 3C. 3C refers to the current value at which the battery capacity is fully discharged in 10 / 3 hours.

[0227] In the case of investigating the second type of cycle characteristics, except that the storage time of the secondary battery is changed to 12 months, the capacity retention rate 2 (%), another indicator for evaluating cycle characteristics, is calculated by following the same steps as in the case of investigating the first type of cycle characteristics.

[0228] [Table 1]

[0229]

[0230] [Table 2]

[0231]

[0232] [Table 3]

[0233]

[0234] [Inspection]

[0235] As shown in Tables 1 to 3, the resistance change rate and capacity retention rates 1 and 2 of secondary batteries containing chain carboxylic acid esters in the electrolyte (solvent) vary significantly depending on the content (X, Y, and content ratio Z) of the coating 22C.

[0236] Specifically, physical property conditions 1~3 are met at different times (content X=11μmol / m). 2 ~22μmol / m 2 Content Y = 7 μmol / m 2 ~13μmol / m 2 In the case of ratios Z=1.2~2.1 (Comparative Examples 1~9), a trade-off occurs where an improvement in either the rate of change of resistance or the capacity retention rate 1 or 2 results in a deterioration in all other rates. Therefore, it is impossible to improve both the rate of change of resistance and the capacity retention rate 1 or 2.

[0237] In contrast, when physical property conditions 1 to 3 are satisfied simultaneously (Examples 1 to 13), the aforementioned trade-off is broken, thus improving both the rate of change of resistance and the capacity retention rates 1 and 2.

[0238] In particular, when physical property conditions 1 to 3 are simultaneously satisfied, the following tendencies are observed: First, when propyl propionate is used as a chain carboxylic acid ester, both the rate of change in electrical resistance and the capacity retention rates 1 and 2 are sufficiently improved. Second, when a cyclic sulfonate ester is used as a sulfur-containing compound, both the rate of change in electrical resistance and the capacity retention rates 1 and 2 are sufficiently improved.

[0239] <Examples 14-17>

[0240] Aside from changing the type of sulfur-containing compound, a secondary battery was manufactured using the same steps, and its battery characteristics were then evaluated. New sulfur-containing compounds used included propenyl sulfonyl lactone (PRS) as a cyclic sulfonate, propargyl methanesulfonate (PMS) as a chain sulfonate, propane disulfonic anhydride (PSAH) as a cyclic disulfonic anhydride, and sulfonyl propionic anhydride (SPAH) as a cyclic sulfonic acid carboxylic anhydride.

[0241] [Table 4]

[0242]

[0243] As shown in Table 4, even with changes in the type of sulfur-containing compound, the same results as in Tables 1-3 are obtained. That is, if physical property conditions 1-3 are satisfied simultaneously, the rate of change of resistivity and the capacity retention rates 1 and 2 can all be improved.

[0244] [Summarize]

[0245] According to the results shown in Tables 1 to 4, when the coating 22C of the negative electrode 22 contains sulfur as a constituent element, the electrolyte contains chain carboxylic acid esters, and physical property conditions 1 to 3 are simultaneously met, the rate of change of resistance and the capacity retention rates 1 and 2 are all improved. Therefore, excellent resistance characteristics and excellent cycle characteristics are obtained in the secondary battery.

[0246] The above description, which presents the present technology through one embodiment and example, does not limit the structure of the present technology to the structure described in one embodiment and example, and therefore allows for various modifications.

[0247] Specifically, the case where the secondary battery structure is a laminated film type has been described. However, the battery structure of a secondary battery is not particularly limited, and can therefore be cylindrical, square, coin-shaped, button-shaped, etc.

[0248] Furthermore, while the structure of the battery element has been described as either wound or stacked, since the structure of the battery element is not particularly limited, it can also be a repeatedly folded type, such as folding the positive and negative electrodes into a Z-shape.

[0249] Furthermore, while the use of lithium as the electrode reactant has been described, this electrode reactant is not particularly limited. Specifically, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, the electrode reactant can also be other light metals such as aluminum.

[0250] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described herein. Thus, other effects can also be obtained with this technology.

Claims

1. A secondary battery, It includes a positive electrode, a negative electrode, negative electrode wiring connected to the negative electrode, and an electrolyte. The negative electrode includes a negative electrode active material layer and a coating covering the surface of the negative electrode active material layer. The coating contains sulfur as a constituent element. The electrolyte contains chain-like carboxylic acid esters. The coating is divided into three equal parts—a first coating portion, a second coating portion, and a third coating portion—in a direction away from the negative electrode wiring. The sulfur content of at least one of the first coated portion and the third coated portion is 11 μmol / m³. 2 Above and 22 μmol / m 2 the following, The sulfur content in the second coated portion is 7 μmol / m 2 Above and 13 μmol / m 2 the following, The ratio of the sulfur content in at least one of the first coating portion and the third coating portion to the sulfur content in the second coating portion is 1.2 or more and 2.1 or less.

2. The secondary battery according to claim 1, wherein, The chain carboxylic acid ester contains at least one of ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate.

3. The secondary battery according to claim 1 or 2, wherein, The electrolyte also contains sulfur-containing compounds.

4. The secondary battery according to claim 3, wherein, The sulfur-containing compound contains at least one of cyclic sulfonates, chain sulfonates, cyclic disulfonic anhydrides, and cyclic sulfonic acid carboxylic anhydrides.

5. The secondary battery according to any one of claims 1, 2, or 4, The secondary battery is a lithium-ion secondary battery.

6. The secondary battery according to claim 3, The secondary battery is a lithium-ion secondary battery.

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